Certain clinical and necropsy findings are described in 56 patients with mitral valve prolapse (MVP): 15 patients, aged 16 to 69 years (mean 39) died suddenly from MVP, and the remaining 41 patients died from other causes. Of the latter 41 patients, 7, aged 17 to 59 (mean 45), had associated congenital heart disease, and 34 patients, aged 17 to 70 (mean 52), had no associated congenital cardiac abnormalities. Compared to the 34 MVP patients without associated congenital heart disease and not dying suddenly from MVP, the 15 patients who died suddenly from MVP were younger (mean age 39 plus or minus 17 years -vs- mean age 52 plus or minus 15 years [p=0.01], were more often women (10/15 (67%] -vs9/34 [26%] [p=0.008]), and had a lower frequency of mitral regurgitation (1/15 [7%) -vs- 13/34 [38%] [P=0.02]). The patients dying suddenly from MVP also were less likely to have evidence of ruptured chordae tendineae (4/14 [29%] -vs- 10/15 (67%] [p=0.04]). The frequency of an increased heart weight (10/15 [67%] -vs17/29 [59%]), a dilated mitral valve anulus (12/15 [80%] -vs- 17/21 [81%]), a dilated tricuspid valve anulus (1/14 [7%] -vs- 4/23 [17%]), an elongated anterior mitral leaflet (12/14 (86%] -vs- 7/13 [54%]), an elongated posterior mitral leaflet (11/14 [79%] -vs- 10/13 [77%]), and a fibrous endocardial plaque under the posterior mitral leaflet (11/15 (73%] -vs- 12/19 [63%] were similar between the 2 groups. The severity of the prolapse (mild, 3/15 [20%] -vs- 2/19 [11%]; moderate 4/15 [27%] -vs- 11/19 [58%], and severe 8/15 [53%] -vs- 6/19 [32%]) also was similar between the 2 groups. Thus, persons with MVP who die suddenly without another recognized cause tend to be relatively young women with associated mitral regurgitation.